For example, in a driving method of a spindle motor of a HDD device, reduction in rotation pulsation is desired strongly. If the rotation pulsation is large, it causes an error in reading or writing, and it is a great obstacle to increase recording density. Furthermore, the rotation pulsation is preferably small as possible to reduce noise generated by the HDD device.
And, in recent years, with advancement in reduction in cost of the HDD, reduction in manufacturing cost of the spindle driving motor is required. Consequently, degradation in manufacturing precision and manufacturing variation are increased, and torque pulsation caused therefrom is becoming a problem.
In such a situation, a method using an ideal sinusoidal current as a driving current waveform of the motor is the mainstream in recent years (Japanese Patent Application Laid-Open Publication No. 2005-102447 (Patent Document 1), for example). If an induced voltage of the motor is assumed to be an ideal sinusoidal wave, the rotation pulsation can be suppressed to zero by driving the motor with a sinusoidal current, in principle.
In reality, however, the induced voltage of the motor is distorted and a pulsation component is generated even in the sinusoidal wave driving. In order to suppress this, in Patent Document 1, the waveform of the applied voltage is corrected so as to be adjusted to match the induced voltage in advance, thereby suppressing generation of the pulsation.
In addition, as a driving method for suppressing the rotation pulsation, a method of tabling a pulsation pattern in advance and correcting the pulsation (Japanese Patent Application Laid-Open Publication No. 11-103588 (Patent Document 2), for example), a method of calculating and estimating a disturbance torque component, which is a cause of pulsation, by an observer and performing control to cancel the disturbance torque component (Japanese Patent Application Laid-Open Publication No. 2001-352789 (Patent Document 3)) and the like are proposed.